This invention relates to interfaces between multi-protocol network host computers and printers on the network. The invention is disclosed particularly in relation to a network adapter circuit having a first physical connection to the multi-protocol computer network, a second physical connection to a printer controller, and an intermediate portion for separately processing print job information and priority information presented in each different network protocol.
In accordance with the embodiment of the invention to be described, a network adapter interfaces between a network of host computers and a printer to communicate priority information in accordance with the Network Printer Alliance Protocol. The published Network Printer Alliance Protocol (NPAP) defines a bi-directional means for communication between a host computer and a printer. The NPAP compliant data and commands are transported under the various network protocols such as TCP/IP.
The details of the NPAP am contained in the NPAP Specification Level 1, Revision N, Feb. 1, 1994. This NPAP Specification is incorporated herein by reference. Copies of the specification are, for example, presently available via anonymous FTP from ftp.lexmark.com [192.146.101.4]. The employment of the NPAP means of communication is described in a number of examples for a single protocol network adapter interface in a commonly assigned U.S. patent application Ser. No. 08/350,860, now U.S. Pat. No. 5,550,957, entitled MULTIPLE VIRTUAL PRINTER NETWORK INTERFACE, filed Dec. 7, 1994, which is also incorporated herein by reference.
In the embodiment to be described hereinafter, the network adapter supports four network protocols: LexLink, Novell NetWare, Apple Talk and TCP/IP. The adapter may receive data from each of these protocols simultaneously, but only one of the protocols may have access to the printer at any one time. This access is called capturing the printer. When one protocol captures the printer (for a print job) the others are buffered until they get their turn. This poses a problem for the timely processing of priority inquiries utilizing NPAP. If these priority requests are processed in the same fashion as print data, the response from the printer may be delayed significantly.
In accordance with one aspect of the invention, the solution to this problem entails having an alternate channel through the network adapter and in the printer that will allow N PAP queries to bypass the print job information. The alternate channel must function so that NPAP priority information can bypass print data whether the print data is from that network protocol or another network protocol so that the priority information can be processed immediately. In practice, an alternate channel of communication is provided through each module of network protocol code employed by the network adapter.